Corrosion inhibition coating composition



Patented Aug. 29, 1944 CORROSION INHIBITION COATING COMPOSITION AaronWachter, San Francisco, Calif., assignor to Shell Development Company,San Francisco, Calif., a corporation of Delaware N Drawing. ApplicationJuly 22, 1941, Serial No. 403,533

Claims. (01. 44-72 The present invention relates to corrosion preventioncoatings and more specifically to coatings for preventing corrosion ofmetal surfaces by the water often associated in small amounts withwater-immisible liquids.

In the storage and handling of various waterimmiscible liquid materials,particularly hydrocarbons it is often necessary both to transport and/orto store such materials in metal containers, as in steel drums or tanksand thelike. Since these materials often contain varying amounts ofwater in solution or in suspension, which may separate clue totemperature changes for example, internal corrosion of the container bythe water almost always occurs to a greater or lesser degree. Thisproblem is particularly serious when gasoline is under consideration. Inspite of all reasonable and practicable precautions during themanufacture of gasoline, when the same is stored in drums or tanks for aperiod, especially as is so often practiced in handling aviationgasoline, an appreciable amount of water separates and will be found asa film or in minute droplets on the container Walls or even in smallpools in the bottom of thecontainer. This of course brings about idealconditions for corrosion and consequent damage to the container as Wellas the even more serious contamination of the gasoline or similarproduct stored within the container.

It is to be clearly understood that the corrosion inhibiting coatingdescribed below is intended for use only in those cases in whichrelatively small quantities of water come in contact with the surfacesto be protected, as distinguished from primarily aqueous systems, suchas water tanks, etc.

. As a result of the above described corrosion, it has become necessaryfor manufacturers .and shippers of such products to apply variousinternal coatings to the walls of such containers or to add corrosioninhibitors of one type or another to the product being stored.

It is an object of the present invention to provide an improved internalcoating for containers which are to be used as described above.. It is afurther object of this invention to provide an internal coating whichwill both prevent corrosion and remove to a large extent any corrosionproducts already present in material which may be transferred tocontainers protected with the hereinafter described improved coating.Another object is to provide an internal container coating which willprevent contact between the container walls and the material storedtherein, thus preventing corrosion of the container by materials whichmay be dissolved in the stored material, such as organic acids andsulfur compounds. Further objects are to supply a coating which isinexpensive, easily applied and removed, and

which does not contaminate in any way materials stored in containersprotected by the same.

Broadly, the present improved coating oompr ises a hydrocarboninsoluble, water-soluble mucilaginous material, a plasticizer ifnecessary, and sodium nitrate. By mucilaginous material is meant thosematerials which either alone or in the presence of a suitableplasticizer provide a continuous, pliable film when applied in solutionand the solvent removed therefrom. Most of the proteins andcarbohydrates of animal and vegetable origin and products derivedtherefrom fall within the limits of this definition. For example, puregrades of the following types of compounds and mixtures of the same willbe found suitable: proteins, albuminoids, glues, gelatins,phosphoproteins, caseins, sugars, starches, dextrins, gums and cellulosederivatives. More specifically, the following compounds are among thosesuitable as the mucilaginousbase material in the presently disclosedcoating: corn starch (partially hydrolyzed) molasses, gum arabic,agar-agar, dextrin, pectin, barley sugar, caramel, xylan, wheat glutenand gum tragacanth.

As a specific example and in a preferred embodiment of the invention,the following composition has been found especially satisfactory:

Per cent by weight, approximately.

Dextrin 60 Glycerin 30 Inhibitor 10 identical tests were severelycorroded and their contents so thoroughly contaminated as to bepractically 'valueless without recovery treatment.

The coating is preferably applied'by spraying a quantity of the 40%solution into the container and drawing ofi any excess before drying,although other methods such as brush application in large storage tanksmay be utilized if desired. In any .case, application conditions shouldbe adjusted to provide at least approximatelyt milligrams of dehydratedcoating per square inch of surface to be protected. A usuallysatisfactory coating is attained if from 1 to 2 fluid ounces of the 40%solution are sprayed into a 55 gallon drum, in a manner to cover allinternal surfaces, the drum then being subjected to a temperature ofabout 250. F. for approximately 5 minutes.

This process may be easily included in the commonly employed drumcleaning treatment wherein dirty drums are washed with a hot alkalinesolution, rinsed, steamed, dried and heated prior to painting theexterior surfaces. After the drums have been dried, the abovedescribed'coat- 1 ing may be applied and the drums passed on to theheating stage in the usual manner. The washing steps will remove alltraces of a previous protective coating if such has been applied.

Although glycerin is the preferred plasticizer for use in the presentcoating, glycol and other hydrocarbon insoluble polyhydric alcohols,glycerinpolymers, amines, hydroxy amines, hydroxy 'ethers, and similarmaterials which have known plasticizing properties will also usually befound satisfactory.

The amounts of the various components of the coating may be variedwithin certain limits without deleterious effects. The formula givenabove, i. e. base, plasticizer and inhibitor in the approximateproportions of 60:30:10 has been found to be generally satisfactory fornormal conditions of service and in fact includes an appreciable safetyfactor in the quantity of inhibitor incorporated. Sodium nitrite, forexample, is known to be an efficient inhibitor at concentrations as lowas .02%'; however, in view of the relatively small quantities actuallyused in employing the preferred formula (1.5 grams in a-55 gallon drum)and in order to obivate completely any danger of localized corrosion dueto the possibility of a relatively large pool of water occurring in thecontainer, it is considered preferable to employ a reasonable excess ofinhibitor. The relative proportions of base and plasticizer used will ofnecessity vary with the specific materials utilized.

In the case where dextrin is used as a base and glycerin as aplasticizer, from approximately 40% to 85% dextrin, the balance beingglycerin and inhibitor (from .02 to has been found satisfactory.

As has been mentioned above, the inhibitor coating is applied insolution, water being the preferred solvent. A solution containing 40%by portions noted:

Per cent by weight,

approximately Arrowroot starch Glycerin 85 Sodium nitr 10 In thisformula, the quantity of starch may be varied from approximately .5% byweight to approximately 10% by weight. Notless .than approximately 60%by weight of glycerin should be used, however, or an unsatisfactorycoating will result. This composition is preferably applied in anapproximately solution in water.

Another coating which has been found suitable is formulated as follows:

Per cent by weight,

approximately Liquid glue (animal) 80 Glycerin g 10 Sodium nitri 10amounts of water against corrosion comprising I from 40% to 85% byweight of dextrin, at least .02% by weight sodium nitrite and thebalance a water-soluble polyhydric alcohol.

2. A water-soluble corrosion inhibiting coating composition suitable forprotecting metal surfaces in contact with hydrocarbons containing smallamounts of water against corrosion comprising approximately by weightofdextrin, approx,- imately 30% by weight of a water-soluble polyhydricalcohol and the balance sodium nitrite, said coating having a pH of atleast 6 in water solution.

3. A water-soluble corrosion inhibiting coating composition suitable forprotecting metal surfaces in contact with hydrocarbons containing smallamounts of water against corrosion comprising about 5-80% by weight of awater-soluble hydrocarbon-insoluble mucilaginous base, about 1085% byweight of a water-soluble polyhydric alcohol, and about .02 to 10% byweight of sodium nitrite.

4. A water-soluble corrosion inhibiting coating composition suitable forprotecting metal surfaces in contact with hydrocarbons containing smallamounts of water against corrosion comprising about 51-80% by weight ofa water-soluble hydrocarbon-insoluble mucilaginous base, about 10-85% byweight of a water-soluble polyhydric alcohol, and at least .02% byweight of sodium nitrite. .7

5. A water-soluble corrosion inhibiting coating composition suitable forprotecting metal surfaces in contact with hydrocarbons containing smallamounts of water against corrosion comprising from 40% to by weight ofdextrin, at least .02% by weight of sodium nitrite and the balanceglycerin.

AARON WACHTER.

